Cast Nazgûl by paying .
Nazgûl enters, triggering its first activated ability, causing the Ring to tempt you; choose Nazgûl as your Ring-bearer, making it legendary.
Nazgûl's second activated ability triggers, putting a +1/+1 counter on each Wraith you control.
Activate Ashnod's Altar by sacrificing Nazgûl, adding .
Ratadrabik of Urborg triggers, creating a token copy of Nazgûl that's a 2/2 Zombie.
Repeat from step 2.

Cast Nazgûl by paying .
Nazgûl enters, triggering its first activated ability, causing the Ring to tempt you; choose Nazgûl as your Ring-bearer, making it legendary.
Nazgûl's second activated ability triggers, putting a +1/+1 counter on each Wraith you control.
Activate Viscera Seer by sacrificing Nazgûl.
Ratadrabik of Urborg triggers, creating a token copy of Nazgûl that's a 2/2 Zombie.
Resolve the ability from step 4, scrying 1.
Repeat from step 2.

Cast Nazgûl by paying .
Nazgûl enters, triggering its first activated ability, causing the Ring to tempt you; choose Nazgûl as your Ring-bearer, making it legendary.
Nazgûl's second activated ability triggers, putting a +1/+1 counter on each Wraith you control.
Activate Altar of Dementia by sacrificing Nazgûl.
Ratadrabik of Urborg triggers, creating a token copy of Nazgûl that's a 2/2 Zombie.
Resolve the ability from step 4, milling target player equal to the sacrificed creature's power.
Repeat from step 2.

Cast Nazgûl by paying .
Nazgûl enters, triggering its first activated ability, causing the Ring to tempt you; choose Nazgûl as your Ring-bearer, making it legendary.
Nazgûl's second activated ability triggers, putting a +1/+1 counter on each Wraith you control.
Activate Phyrexian Altar by sacrificing Nazgûl, adding one mana of any color.
Ratadrabik of Urborg triggers, creating a token copy of Nazgûl that's a 2/2 Zombie.
Repeat from step 2.

Cast Nazgûl by paying .
Nazgûl enters, triggering its first activated ability, causing the Ring to tempt you; choose Nazgûl as your Ring-bearer, making it legendary.
Nazgûl's second activated ability triggers, putting a +1/+1 counter on each Wraith you control.
Activate Bartolomé del Presidio by sacrificing Nazgûl.
Ratadrabik of Urborg triggers, creating a token copy of Nazgûl that's a 2/2 Zombie.
Resolve the ability from step 4, putting a +1/+1 counter on Bartolomé del Presidio.
Repeat from step 2.

Cast Nazgûl by paying .
Nazgûl enters, triggering its first activated ability, causing the Ring to tempt you; choose Nazgûl as your Ring-bearer, making it legendary.
Nazgûl's second activated ability triggers, putting a +1/+1 counter on each Wraith you control.
Activate Carrion Feeder by sacrificing Nazgûl.
Ratadrabik of Urborg triggers, creating a token copy of Nazgûl that's a 2/2 Zombie.
Resolve the ability from step 4, putting a +1/+1 counter on Carrion Feeder.
Repeat from step 2.

Cast Nazgûl by paying .
Nazgûl enters, triggering its first activated ability, causing the Ring to tempt you; choose Nazgûl as your Ring-bearer, making it legendary.
Nazgûl's second activated ability triggers, putting a +1/+1 counter on each Wraith you control.
Activate Yahenni by sacrificing Nazgûl.
Ratadrabik of Urborg triggers, creating a token copy of Nazgûl that's a 2/2 Zombie.
Resolve the ability from step 4, giving Yahenni indestructible until end of turn.
Repeat from step 2.

Cast Nazgûl by paying .
Nazgûl enters, triggering its first activated ability and Blasting Station.
Resolve Blasting Station's ability, untapping it.
Resolve Nazgûl's ability, causing the Ring to tempt you; choose Nazgûl as your Ring-bearer, making it legendary.
Nazgûl's second activated ability triggers, putting a +1/+1 counter on each Wraith you control.
Activate Blasting Station by sacrificing Nazgûl.
Ratadrabik of Urborg triggers, creating a token copy of Nazgûl that's a 2/2 Zombie.
Resolve the ability from step 6, dealing 1 damage to any target.
Repeat from step 2.

Cast Nazgûl by paying .
Nazgûl enters, triggering its first activated ability, causing the Ring to tempt you; choose Nazgûl as your Ring-bearer, making it legendary.
Nazgûl's second activated ability triggers, putting a +1/+1 counter on each Wraith you control.
Activate Woe Strider by sacrificing Nazgûl.
Ratadrabik of Urborg triggers, creating a token copy of Nazgûl that's a 2/2 Zombie.
Resolve the ability from step 4, scrying 1.
Repeat from step 2.

Cast Nazgûl by paying .
Nazgûl enters, triggering its first activated ability, causing the Ring to tempt you; choose Nazgûl as your Ring-bearer, making it legendary.
Nazgûl's second activated ability triggers, putting a +1/+1 counter on each Wraith you control.
Activate Bloodflow Connoisseur by sacrificing Nazgûl.
Ratadrabik of Urborg triggers, creating a token copy of Nazgûl that's a 2/2 Zombie.
Resolve the ability from step 4, putting a +1/+1 counter on Bloodflow Connoisseur.
Repeat from step 2.

Xavier Sal does not have summoning sickness.
You have a way to create a token copy of Nazgûl.

Create a token copy of Nazgûl.
When the Nazgûl token enters the battlefield, its first ability and Intruder Alarm trigger.
Resolve the Intruder Alarm trigger, untapping all creatures.
Resolve the Nazgûl trigger, causing the Ring to tempt you.
Each Nazgûl's second ability triggers, putting that many +1/+1 counters on each Wraith you control.
Activate Xavier Sal's first ability by tapping it and removing a counter from a permanent you control, creating a copy of the Nazgûl token.
Repeat from step 2.

Once you have infinite +1/+1 counters on Wraiths you control, you can instead create copies of any other creature token(s) you control.

Cast Nazgûl by paying .
Nazgûl enters, triggering its first activated ability, causing the Ring to tempt you; choose Nazgûl as your Ring-bearer, making it legendary.
Nazgûl's second activated ability triggers, putting a +1/+1 counter on each Wraith you control.
Activate Goblin Bombardment by sacrificing Nazgûl.
Ratadrabik of Urborg triggers, creating a token copy of Nazgûl that's a 2/2 Zombie.
Resolve the ability from step 4, dealing 1 damage to any target.
Repeat from step 2.

Cast Nazgûl by paying .
Nazgûl enters, triggering its first activated ability, causing the Ring to tempt you; choose Nazgûl as your Ring-bearer, making it legendary.
Nazgûl's second activated ability triggers, putting a +1/+1 counter on each Wraith you control.
Activate Thermopod by sacrificing Nazgûl, adding .
Ratadrabik of Urborg triggers, creating a token copy of Nazgûl that's a 2/2 Zombie.
Repeat from step 2.